LECTURE 20- Hormone: regulators of development II

what hormones play a role in seed germination

gibberellins (GA) and abscisic acid (ABA)

what hormones play a role in seedling development

Ethylene and Gibberellins (GA)

what hormones play a role in plant development and elongation

Auxin (AUX)

what hormones play a role in maintaining meristem cells

Auxin (AUX), Gibberellins (GA) and cytokinins (CK)

what hormones play a role in floral meristem development/flowering

Gibberellins (GA), cytokinins (CK) and auxin (AUX)

what’s the process for hormone response in plants

1. environmental or developmental signal

2. hormones biosynthesise at the site of synthesis

3. hormones are transported where needed

4. hormones cause a response in the plant

what are examples of environmental signals

• light (photosynthesis)

• herbivory (plants produce hormone to become less tasty to herbivores)

• drought (stomata closes to preserve water)

what are other kinds of plant hormones

• Brassinolides: cell elongation/division

• Salicylic acid: plant defence

• Jasmonates: plant defence + growth regulation

• Signalling peptide systemin: 18 amino acids, herbivore defence

• Strigolactones: branching and symbiotic arbuscular mycorrhizal fungi

• Florigen: flowering

what is the most common kind of auxin

IAA: naturally produced auxin

which auxin is synthetic

2,4-D

where is auxin primarily made

in lead primordia and young leaves (also root + shoot meristems)

how is auxin transported

 both polar(unidirectional) and non-polar ways

what effects does auxin have

• Apical dominance (side shoots in plants, when main meristem is removed)

• Tropic responses (when plant grows towards light)

• Vascular tissue differentiation

• Promoting cambial activity

• Root + shoot growth

• Leaf and fruit abscission

• Stimulating ethylene

• Flowering

• Fruit development

how does polar auxin transport work

1. IAA is negatively charged in the cytoplasm (IAA-)

2. IAA- transported outside of cell and enters lower pH environment

3. IAA- becomes IAAH and is non charged, and can pass through cell’s semi-permeable membrane

4. IAAH loses a proton becomes IAA- again inside the cell, and becomes trapped in the cell

there’s also a pump inside the cell that pumps IAA- into the cell

diffusion moves IAA- downwards and out of the cell. process repeats

how does xylem regeneration occur with auxin

• auxin travels downwards from plant apex

• if plant apex is cut off, there is no more auxin being produced

• if you put auxin-filled paste on cut off parts, auxin will differentiate tissue and produce vascular tissue to repair wound

how does auxin help roots

auxin helps to maintain root meristems and root development

how does auxin move in roots

1. auxin moves down through active polar transport

2. auxin maximum is created at bottom of root

3. auxin travels back up root along the sides

how does auxin help with fruit development

auxin is produced in seeds and helps with fruit development

• when seeds are removed from a plant, the auxin is removed and the plant stops growing in that area